The dual-active full-bridge converter based on phase-shifting control technology (Dual Active Bridge-Isolated Bidirectional DC/DC Converter, DAB) has the advantages of high-power density, fast dynamic response, easy to realize soft switching, and bidirectional flow of power, etc. It is widely welcomed in the fields of uninterruptible power supply, electric vehicles, and solid-state transformers. The common DAB converter control method is phase shifting control, which generates a two-level or multi-level voltage square wave with relative phase shift at the primary side port and the secondary side port of the high-frequency transformer, at the same time, the relative phase shift of the square wave at the primary and secondary sides and the duty ratio of each level are adjusted to regulate the power flow through the converter and control the waveform of the current flow through the high-frequency transformer. In the traditional two-level DAB converter, commonly used modulation methods are single phase shift modulation (SPSM), dual phase shift modulation (DPSM), extended phase shift modulation (EPSM), and triple phase shift modulation (TPSM). Among the methods, TPSM has three independent control variables and is the most flexible modulation mode in the two-level DAB converter. However, when the port voltage of the converter changes within a large range, such as power battery voltage of the vehicle can sometimes vary from 200V to 450V, in such applications, even with the optimized TPSM modulation technology, the two-level DAB converter still has large current stress and current root mean square (RMS) value in some working areas, low energy transmission efficiency, and its comprehensive performance still needs to be further improved.
To adapt the converter to a wider range of port voltage, the diode clamp mixed three-level DAB converter can be added with an intermediate level with controllable duty ratio and obtain an additional independent control variable, which breaks the design limit of the traditional two-level DAB converter, improves the conversion efficiency of the input and output power over the entire voltage range and power range, and achieves global optimal operation. However, how to determine the duty ratio of different levels and how to coordinate the four independent control variables to reduce the current stress and the current root mean square (RMS) value of the isolated transformer in the converter is an urgent problem to be solved in the topology construction and control method of the diode clamp mixed three-level DAB converter.
At present, there is no description or report of similar technology to the present invention, and no similar data at home and abroad have been collected.